(a) Technical Field
The present disclosure relates to a system and method for controlling energy in a vehicle. More particularly, the present disclosure relates to a system and method for controlling energy of an eco-friendly vehicle that effectively discharges the voltage at an inverter DC link terminal, restores energy consumed due to high-voltage discharge, and efficiently uses energy of a vehicle.
(b) Background Art
Currently, common internal combustion engine vehicles that use fossil fuels such as gasoline or diesel cause environmental contamination due to exhaust gas, global warming due to carbon dioxide emissions, and induction of respiratory disease due to generation of ozone. Eco-friendly vehicles such as an Electric Vehicle (EV) that runs by operating an electric motor, a Hybrid Electric vehicle (HEV) that runs using an engine and an electric motor, and a Fuel Cell Electric Vehicle (FCEV) that runs by operating an electric motor, that use power generated by a fuel cell have been developed.
The eco-friendly vehicles are low emission vehicles, that minimize the environmental problem and the problem of exhaustion of natural resource, or zero emission vehicles. As shown in FIG. 1, these vehicles include an electric motor (e.g., driving motor) 30 for driving the vehicles and a high-voltage battery (e.g., main battery) 10 that is an electricity accumulation unit that supplies power to the electric motor 30, and further include an inverter 21 that operates the electric motor 30.
In the FCEV, an electricity accumulation unit such as a battery is used as a secondary power source in parallel with a fuel cell, which is the main power source, and fuel cell hybrid systems including a supercapacitor as a secondary power source other than a battery have also been developed.
The inverter 21, which drives an electric motor (hereafter, referred to as ‘driving Motor’) 30 by changing the phase of power supplied from a high-voltage battery 10 (or fuel cell), converts direct current (DC) voltage of a high-voltage battery into three-phase alternating current (AC) power and then supplies the power as the driving power for the driving motor.
In FIG. 1, the reference numeral ‘20’ indicates a Motor Control Unit (MCU) that drives phase conversion by switching devices S in the inverter 21 in Pulse Width Modulation (PWM). Further, the eco-friendly vehicles are mounted with a power conversion system, for example, with the high-voltage battery 10, and a Low Voltage DC-DC Converter (LDC) 40 for DC-DC power conversion between a low-voltage battery (e.g., 12V secondary battery) 50 and a low-voltage auxiliary electric load.
Accordingly, the eco-friendly vehicles such as HEVs and EVs use two batteries of the high-voltage battery 10 used as a high-voltage main power source and a 12V auxiliary battery for common vehicles used as a 12V power source, in which the high-voltage battery 10 supplies power to a driving system (e.g., driving motor), an air conditioner, or a heater and the 12V auxiliary battery 50 supplies power to the low-voltage electric loads in the vehicles, similar to the system in common vehicles. When the power of the auxiliary battery 50 is insufficient, the auxiliary battery is charged by the LDC 40.
On the other hand, during a collision of a vehicle, an electric shock accident may occur due to electric connection between a high-voltage battery and a driver, and therefore a technology of a forced high voltage discharge has been used in the related art to remove the danger of the high-voltage shock.
FIG. 2 is an exemplary flowchart illustrating a forcible discharge logic of the related art. Referring to FIG. 2, when a key-off or an airbag operation signal (e.g., collision signal) is sensed, a controller (e.g., HPCU) fixes interlock situation (S1) and transmits a signal requesting main relay off to a battery controller (hereafter, referred to as a battery management system ‘BMS’). The battery controller turns off a main relay 11 within a predetermined time and transmits the off-state of the main relay 11 to power conversion controllers (MCU, etc.) (S2).
The voltage of a DC capacitor C is forcibly discharged from the point of time (S3), in which the motor control unit (hereafter, referred to as an ‘MCU’) 20 performs forcible discharge that the capacitor voltage is discharged to the driving motor 30 by switching control of a switching device S in the inverter 21.
Furthermore, the d-axis current, not the q-axis current, is applied as much as possible to the driving motor 30 (zero torque control of a motor). However, the type of forcible discharge of the related art consumes energy stored in the capacitor C of the inverter 21 without restoring energy.
On the other hand, in the eco-friendly vehicles, the battery power is supplied to power conversion systems (e.g., inverter, LDC, etc.) such as the inverter 21 and the LDC 40 via a DC junction box 60 and various relays and fuses, including a PRA (Power Relay Assembly) such as the main relay 11 controlled to be on/off by a BMS (Battery Management System), are disposed within the junction box 60 (e.g., the main relay is separated from the junction box in FIG. 1). However, since the power conversion systems and the DC junction box share the high-voltage power source via a connector, when the connector that is connected to the junction box is mistakenly separated while the engine is operating, an electric shock accident may occur due to electric connection between the high-voltage battery power and the human body.
When forcible discharge through the inverter is performed in removal of the connector to take precautions against the danger, the energy stored in the capacitor C is consumed without being restored. Further, torque may be generated in the driving motor 30 due to an angular error of a rotation sensor in the forcible separation through the inverter 21, and thus, when the driver separates the connector to examine the vehicle, there is the possibility that the vehicle may start and injury.
The above information disclosed in this section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.